1. Field
The disclosed subject matter relates generally to compositions and processes used in the recovery of value minerals from mineral ore bodies. More particularly, the disclosed subject matter relates to froth flotation processes that utilize an organic ammonium salt of a sulfur-containing acid as a value mineral collector.
2. State of the Art
Froth flotation is a widely used process for beneficiating ores containing valuable minerals, often referred to as “value minerals”. Value mineral(s) refer to the metal, metals, mineral or minerals that are the primary object of the flotation process, i.e., the metals and minerals from which it is desirable to remove impurities.
A typical froth flotation process involves intermixing an aqueous slurry that contains finely ground ore particles with a frothing or foaming agent to produce a froth. Ore particles that contain the value mineral(s) are preferentially attracted to the froth because of an affinity between the froth and the exposed mineral on the surfaces of the ore particles. The resulting beneficiated minerals are then collected by separating them from the froth. Chemical reagents, referred to as “collectors,” are commonly added to the froth flotation process to effect the separation. Certain theory and practice indicates that success of a flotation process for base metal sulfide and precious metal ores is dependent on the collectors which impart selective hydrophobicity to the value mineral separated from other minerals. See, e.g., U.S. Pat. No. 4,584,097, the entirety of which is incorporated by reference herein.
Other reagents, such as “frothers”, may be added to the process to provide a suitable basic froth phase to capture hydrophobic value minerals and facilitate separation and recovery thereof. Certain other reagents, referred to as “modifiers”, may be used to enhance separation and recovery of the desired minerals and/or metals. Modifiers, which can include pH regulators, may be used to modify and control the pH of the ore pulp in order to enhance separation and recovery of the desired minerals and/or metals. In some instances, compounds referred to as “activators,” such as copper sulfate, may be used to activate a certain value sulfide mineral in order to enhance collector coating on this sulfide mineral.
Froth flotation is especially useful for separating finely ground value minerals from the associate gangue or for separating value minerals from one another. Because of the large scale on which mining operations are typically conducted, and the large difference in value between the desired minerals and the associated gangue, even relatively small increases in separation efficiency provide substantial gains in productivity. Additionally, the large quantities of chemicals used in mining and mineral processing pose a significant challenge in terms of health and safety to humans and the environment. Consequently, the industry is continually searching for effective alternatives that increase safety while lessening the impact on the environment.
Currently, a large variety of organic sulfur-containing compounds, such as xanthates, dithiophosphates, dithiocarbamates, etc, are utilized as collectors in the flotation recovery of value minerals from sulfide and precious metal ores. Existing thought about such compounds is that either the free acid or any salt of the acid can be used in flotation, and that all the salts and free acid are equivalent, and obtain substantially the same result. Moreover, most of the collectors based on organic sulfur-containing salts are aqueous and are the sodium or potassium salts of sulfur-containing acid. Thus, when names of collectors are mentioned, such as a xanthate or dithiophosphate, it is in reference to a sodium or potassium salt.
A commonly used collector, xanthic acid, is an ionic compound that is produced and transported as solid sodium or potassium salts of xanthic acid and is used as aqueous solutions at the mine site. While they have shown value in mining processes, xanthates oxidize and hydrolyze in the presence of water thereby releasing hazardous byproducts, and causing reduction in metallurgical performance, such as reduction in value mineral recovery and/or grade. Solid xanthate can pose a fire hazard. Other common water-soluble ionic collectors pose similar hazards to a varying degree and display reduced metallurgical performance. An additional hazard is when such aqueous collectors are mixed with other collectors, some toxic gases may be generated, or precipitates can be formed, which reduce the activity of the available collector or form some other undesirable reaction products, all of which also cause reduced metallurgical performance.
Many current collector and formulations thereof do contain water, which reduces the available active collector and contributes significantly to transportation costs. Given the recent increase in fuel costs, cost-effective transportation and energy savings are important in developing alternatives to current collectors.
In view of the foregoing, there is a need in the art to develop a stable collector formulation that offers improved metallurgical performance, cost savings, as well as reductions in hazards to humans and the environment. The inventors of the instant invention believe the subject matter disclosed and claimed herein is an answer to those needs.